The installation of the ENIAC, at the Ballistic Research Laboratories of the U. S. Army Ordnance Corps marked the
beginning of the widespread use of electronic computing machines. Since the advent of the ENIAC, a large expansion has taken
place in the computer field. Investment rates in computing equipment in the United States have risen from ten million dollars
per year in 1953 to one hundred million dollars per year in 1956. Present expenditures for computing equipment has passed
the billion dollars per year mark.

Almost every commodity industry such as oil, steel and rubber is utilizing computing equipment for both scientific and
commercial applications. Service industries, such as banking, transportation, and insurance have applied large scale systems
toward the solution of problems in the fields of accounting, reservations control, and bookkeeping. Manufacturers have used
computing systems for design engineering and scientific research. Many systems are being utilized for inventory and stock
control. The determination of manufacturing plant location and stock parts storage are being made by linear programming
methods. Electronic computers are being utilized by the construction industry for design and location of structures and road
nets. Many digital computers form a part of closed loop industrial process control systems.

Many problems require the processing of large quantities of data, such as is obtained from missile tracking,
telemetering, mineral deposit prospecting and record keeping. The use of electronic computing equipment permits the
processing of large quantities of such data over relatively short periods of time.

Many "on-line" applications of both general and special purpose computers are being made. These control
applications include such examples as control of wind tunnel testing and continuous-flow manufacturing. Computers are
being used for aircraft and missile fire and flight control, both as ground based and missile borne systems.

A discussion of applications of specific systems will be found under the sub-heading "APPLICATIONS" in the various
computing systems descriptions given in Chapter II.

address codes), the command, and perhaps spares, tags, or check digits. For example, the ORDVAC utilizes 39 bits plus sign for an
information word. One-half
of a word, or 20 bits, is subdivided into a 12-bit address portion (for 4,096 high speed storage locations), a 6 bit command
portion for 64 commands, and a 2-
bit spare digit portion for special applications and versatility. The variation of word length among existing systems is rather
wide. Table III shows the word
lengths of the 222 systems described in Chapter II, in ascending order of magnitude. The average or nominal word length for fixed
word length machines is
approximately 40 binary or 12 decimal digits.

Number of Instructions Per Word
In many systems the machine word structure permits several instructions to be expressed by a single word. Of 171 systems,107 were
reported as
operating on a one instruction per word basis and 28 were reported as operating on a two instructions per word basis. Several
systems required two words
to express a complete instruction and, in some systems, several instructions could be expressed by a single word, at the option of
the programmer.

Arithmetic System
Most of the earlier machines operated on a fixed point arithmetic system. The binary or decimal point was arbitrarily fixed at
either the right or left
end of the number. For some systems a centered decimal point permitted the direct expression of whole and fractional parts of
numbers. Scaling is required,
for example, when a decimal or binary point is located at the left end of a number, in which case all quantities must be scaled
between the values of minus
one and plus one.

Many of the later machines were manufactured with built-in automatic floating point equipment, permitting numbers to be expressed
as fractional
parts and exponent parts. The exponent usually is a power of two or ten. Floating point circuitry was added to many of the older
systems. A review of this
sub-heading in the systems descriptions found in Chapter II and an examination of Table III will show the distribution of fixed and
floating point equipment.

Instruction Type
Internally programmed automatic computers require that part of the instruction word be devoted to the address (or addresses) of the
operand (or
operands). The question of how many addresses are to be incorporated into a single word has been answered in many ways. In single
address machines, the
address of one operand is given in the address portion of the instruction word. In two address machines, the address of two
operands are given, for instance
the addresses of the minuend and subtrahend are given for a subtract instruction. For three address machines, the address for
storing the result, e.g., the sum,
difference, product, quotient or square-root, is given. The three address machines usually refer automatically to the next storage
location, in sequence, for the
next three-address instruction word. Machines using the four-address instruction will express the location of two operands, the
location for storing the
results of the operation, and the location of the next instruction, all in one four-address word. In a 1 + 1 system of notation the
address of an operand for the
current instruction is given, along with the address of the next instruction to be performed. Coding for four-address machines is
somewhat simplified,
however, a more complex machine structure is necessary. The following table shows the distribution of different addressing systems
among the types of
computers described in the handbook.

Instruction Word Format
Most systems require adherence to a specific format or sets of formats for preparing coded instructions, in the machine language.
The instruction word
format thus outlines the form in which the instruction is prepared. An accounting must be made of each digit or character of the
instruction word.

continuously recirculated. Information is inserted or read out through the use of standard gating techniques. Among the computers
utilizing acoustic
mercury delay lines are the DYSEAC, EDVAC, ELECOM 725, SEAC and UNIVAC I. Quartz acoustic delay lines were also used. Other types
of delay lines
used for storage of information are the magnetostrictive and the electromagnetic or distributed L-C network. See Tables VI, VII and
VIII, which list the
computing systems utilizing delay line storage units. Although in operating principle there is no difference, it is necessary to
make a distinction between a
delay line used in a storage loop in which information is continuously circulated, and a delay line used only for purposes of
timing the arrival of information
at selected points for performing various logical operations. In the latter, the function is delay, or temporary storage, rather
than permanent storage. Since
delay lines store information serially as a train of electrical or sonic pulses, average random access time is limited to half of
the time length of the delay line
plus the time equivalent to one word length. Because of the serial nature of the system, delay line storage units are limited in
speed. Notice how the delay
line types of systems lie near the bottom of the Access Time of High Speed Storage, Table VI.

The search for shorter access time brought about the development of the electrostatic storage unit, also called the cathode ray
tube storage device.
The material medium in motion was now limited to electrons, i.e., in beams and on charged areas on the screen of a cathode ray
tube. These charged areas
behaved somewhat like an array of charged capacitors. Selection of storage locations and the transfer of information was
efficiently performed by an easily
deflected pencil or beam of electrons which was used for both writing and interrogation. Parallel transfer, in which all digits of
a given word are transferred
simultaneously, became possible with this type of storage system.

The electrostatic storage system, with the inherent problems associated with high accelerating voltages, screen imperfections and
other tube failures,
has all but yielded to the utilization of magnetic cores for the storage of information. A 32 x 32 array of ferrite cores, which
might constitute a typical storage
plane, may measure only a few inches on each side. The cores are placed at the intersection of the wires of a mesh, and a third
winding may be threaded
through all the cores for sensing stored data. The storage takes place in the form of magnetically oriented molecular or atomic
dipoles which retain their
orientation upon removal of the magnetizing force. Many manufacturers intend to
provide computing systems with large capacity core storage units. Advances have been made in the use of perforated ferrite plates
and magnetic films
deposited on glass as a magnetic storage unit. Two such systems, the LINCOLN TX 2 and the UNIVAC 1107 utilize thin films. The
storage principle is the
same as for magnetic cores. Table VI shows the access time of high speed storage units in their approximate relative order of
magnitude for the storage units
used in various computing systems. It must be emphasized that the question of precisely what constitutes access time cannot easily
be resolved unless a
common understanding as to the definition is reached. In the usual sense, one may consider access time as the elapsed time between
the initiation of a
command to transfer an item of information, usually one word, from one address in the storage to another designated register, and
the complete arrival of the
item at the designated location. In many systems, particularly serial storage units, access time depends upon the time location of
the word in the serially
circulating group of words at the instant the transfer command is initiated. For this and other reasons, much misunderstanding can
arise in the consideration of
access time. the data presented in Table VI should therefore be considered to be approximate and should be used with caution.

The capacity of high speed storage units has risen during the past few years as rapidly as access time has diminished. Table VII
shows the capacity
of high speed storage units in terms of numbers of words and word lengths, arranged in relative order of magnitude of equivalent
binary capacity.

Rapid access storage of limited capacity is usually supported by a larger capacity storage unit for a well balanced storage system.
This permits the
transfer of large blocks of information from the rapid access storage unit to the large capacity storage unit for use at another
location or time in the

BRL 1961, ANALYSIS AND TRENDS, start page 1031

computation process. The most prevalent devices for auxiliary storage of this type are the magnetic drum or the magnetic disc. The
access time for large blocks
of information is of the order of tens of milliseconds for most magnetic drum or disc units. Many computing systems utilize
magnetic drums or discs as the
primary storage unit. Several systems utilize large capacity drum or disc units particularly for commercial type applications, such
as payroll, stock inventory,
and personnel records where access times of the order of microseconds are not required. Table IX shows the capacity of various drum
or disc storage systems
currently in use. It should be remembered, when glancing at Table IX, that although an attempt was made to show maximum capability,
additional drum or disc
units can be attached to some systems. Many systems employ magnetic tape as a medium of storage. Although access time is relatively
long because of its
inherently serial nature, a large vole of data can be stored on tape with a high packing density in terms of data units per unit
volume.

The characteristics of a storage device, namely, capacity and access time are two aspects of a storage system which come under
consideration when
designing or using a machine. The user or manufacturer of a system, at times, can trade capacity for access in the sense that under
certain conditions he can
accomplish an equivalent amount of computation with a large capacity, somewhat longer access time system as with a small capacity,
short access time system.
This is the old problem of trading time for space or vice versa. There are limits to this however, for example, when access time
approaches the order of
milliseconds, computation is seriously slowed down. Since large capacity and short access time are features to be desired, let us
examine a quantity determined
by the expression:

1og10 (Capacity in Equivalent Binary Digits/Access Time in Seconds)

In early storage devices, such as music boxes and signal coding equipment, this number is of the order of two to three. Relay
storage units have a number
of the order of four or five. Tube registers of the ENIAC vacuum tube accumulator storage type, enabled this figure to be as high
as 6.3. Magnetic drum
storage units are in the region of 6 to 7. Acoustic delay line storage systems show that this figure is in the range 8.6 to 9.6.
The cathode ray tube storage
(electrostatic) raised the figure as high as 10.79. The magnetic core storage unit permitted an increase of this figure to over 12.
Thin films have now arrived
d on the scene as a practical storage medium. The following table shows the growth, or increase of this number, as development of
computing system
components progressed:

payroll line, a stock item, a set of corresponding test data, etc. There is no doubt that punching cards is a slow process. Paper
tape perforators are also relatively slow in the sense that the data to be punched is usually available at a rate faster than paper
may be mechanically perforated, although high speed perforators are being developed and are finding application. Keyboard
input systems are useful primarily for the manual insertion of words for test or other special purposes.

In addition to paper tape and card readers and punches, many systems utilize high speed printers and magnetic tape units
as a medium of input and output. Magnetic tape output still requires a conversion from magnetic tape to cards or printed page
in order that the information be available to operating personnel. However, since human intervention is gradually being
reduced, the use of magnetic tape for input, output and storage is increasing rapidly. The prevalence of various input-output
media for the 222 computing systems described in this report may be determined by examining the data under the sub-heading
"INPUT" and "OUTPUT" in the systems descriptions given in Chapter II.

One method for decreasing machine time spent waiting for reading and writing instructions to be carried out is to
provide for concurrent operation. The later machines have built-in circuitry for permitting reading and writing to take place
during computations. Apparently the only stipulation is that a given storage location does not become involved in reading,
writing and computing at the same time. Many machines, for example, compute while punching and reading cards or while
"looking-up" information on tape. Others fetch the next instruction out of storage while performing an operation.

Another method of reducing reading and writing time and to avoid a large amount of lost time when a large amount of
machine reading and writing is necessary is to provide for reading and writing on a high speed device such as a magnetic tape or
wire unit and allow "conversion" to another medium to take place off the machine at "leisure". Magnetic tape-to-card
converters and inverters are becoming available as well as magnetic tape-to-printed-page converters. Paper tape and cards may
sometimes be considered as forms of storage, since information recorded on these media may be returned to the machine.
Considerable progress is being made in the field of printed page readers. See, for example, the IBM 1401 System.

It is often necessary to have computing systems capable of communicating with one another directly. For this reason,
input-output media conversion is becoming quite prevalent and large conversion equipment is rapidly becoming available. Input-
output schemes are so many and varied, that a complete treatment of this subject is beyond the scope of this report.

the use of another tube type. This, then increases the number of tube types. Normally, it is, possible to select a type of tube for
a group of duties. In a given system, for example, a certain type is selected for driving, for voltage amplification, for flip-flop
circuits, normally "on" or "off" conditions, etc. This establishes a number of tube types for a given system and any
modification of the system usually should include this "tube type" complement.

The question of crystal diode reliability, diode testing techniques, and diode logical network design, such as individual clamps
versus wired plug-in units, become subjects of interest when diodes are utilized. The quantity of diodes in a given computing
system may be indicative of the nature of the servicing problem, but only when the failure rates, life and circuit demands placed
upon the diode are known. To some extent, malfunctions due to diodes can be aggravated by elevated temperatures. The printed
circuit logical package, containing a specific array of "And" and "Or" gates have become the most prevalent means of
fabrication. The extent of crystal diode use is shown in Table XI.

Many recently developed systems utilize transistors for driving, switching (gating) and other logical functions. Reduced
power and reduced space requirements are advantages of these systems. The question of reliability is rapidly being resolved, as
printed circuits and packaging techniques continue to be improved. Table XII shows the quantity of transistors utilized in the
various computing systems described in Chapter II.

excess of maximum permissable concentrated loadings on some structures. Vibration and shock caused by some equipment such as
tabulators and card
punches can cause trouble in other components. Shock and vibration absorbing pads are required in such cases. When unitized
construction is used, the
weight of a single unit must also be considered when transporting and installing.

Many systems require extensive site preparations. Others may be "plugged in" to any convenient outlet. This topic is adequately
discussed in
the systems descriptions of Chapter II.

An attempt was made to discover whether a "system cost per tube" figure could be established. For the larger systems, the figure is
of the order of
200 dollars per tube installed and for the smaller systems approximately 100 dollars per tube. However, a glance at Tables X and
XIV will show that such a
figure can be calculated with some difficulty. An attempt to determine a figure such as "cost per cubic foot" of electronic
computing equipment would be
equally difficult. Such exercises are left to the reader should such figures be of any interest.

Many computing systems are approaching the age of retirement and replacement. Constant improvements have already
replaced many of the original components of a system. The next few years will see the retirement of many of the older
systems. Such retirement may take the form of salvage of parts, use for educational and training purposes, or scrap. Many older
models are available at reduced prices. A used computer market is developing. In accepting a used computer, one must be
prepared to accept a few headaches. Table XV shows how long some models of computing systems have been in existence.